The 1st Expeditionary Army is the only expeditionary force of the UNSC Army, and is tasked to deliver a prepared UNSC military response to any military or domestic incident that occurs within the Sagittarius-Carina Arm, Orion-Cygnus Arm, or Perseus Arm of the Milky Way Galaxy. The Rangers are comprised of highly modular and mobile task forces that are comprised of infantry, vehicular, and airborne assets, unlike all other frontline Special Forces divisions, which are primarily comprised of infantry elements.